By "supersaturated" with calcium and phosphate is herein meant that higher concentrations of calcium ions and orthophosphate ions are present in the solution than would be present in a saturated solution of those ions.
British patent specification no. GB 1 090 340, published in 1967, discloses compositions for rehardening dental enamel comprising fluoride, calcium, phosphate and sodium chloride which yield, on contact with saliva, supersaturated solutions to form hydroxyapatite. Because saliva is required to form the supersaturated solution, the preferred compositions are in the form of confectionery such as chewing gum. However, it is known that, under most circumstances, saliva is already supersaturated with calcium and phosphate. No disclosure is given of how to make a supersaturated solution ab initio which can then be used effectively in the form of a mouthwash or dental rinse. Furthermore, no mention is made of the possibility of excluding fluoride; or of the formation of octacalcium phosphate by the supersaturated solution in the saliva. In any case, in the absence of or where there is a significantly reduced amount of saliva, these compositions would not work as described.
A supersaturated solution is disclosed in U.S. Pat. No. 5,427,768 which is supersaturated with calcium phosphate and carbon dioxide and used to deposit apatite on the teeth. However, in this case, the supersaturation is caused by release of carbon dioxide, and carbonate is absorbed by the teeth which results in a deposited mineral phase with decreased resistance to dental caries.
British patent specification no. GB 1 408 922, published in 1975, discloses an oral treatment pack which comprises two phases for sequential application to teeth, the isolated phases comprising calcium (50 to 35000 ppm) and phosphate (50 to 40000 ppm) compounds, respectively. However, there is no disclosure or teaching regarding how to make a single phase, supersaturated solution within these concentration ranges which cover four orders of magnitude. Indeed, Example 3 thereof teaches two phases which, if mixed, would result in immediate precipitation of calcium phosphates.
A further solution containing calcium and phosphate is disclosed in British patent specification no. GB 1 509 977, published in 1978. This solution comprises one component containing calcium ions (at least 30 ppm) and another component containing at least 100 ppm fluoride, one or both components also containing phosphate ions (at least 0.1 M) such that on mixing the components hydroxyapatite can be deposited therefrom on teeth. However, such solutions are not stably supersaturated (indeed, this patent teaches that the phosphate ions can be incorporated only in the solution containing calcium ions (at low concentration) which would not allow for the preparation of a stable, non-precipitating, supersaturated solution), and contains greater fluoride than considered to be clinically safe if accidentally swallowed. Again, no reference is made to producing octacalcium phosphate deposits.